System and method for addition and removal of servers in server cluster

ABSTRACT

A method of adding a server to, or removing a server from, a cluster of servers, and of transferring state information. A new server being added sends a message to all existing servers indicating that it is being added, the new server sends a request for state information, the existing servers in the cluster transfer state information to the new server, and the new server sends a commit message to finalize its addition. Acknowledge messages are exchanged during the process. An existing server being removed sends, to the remaining servers, an initiate message, a transfer of state information, and a commit message to finalize the removal, with acknowledge messages exchanged during the process.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims the benefit of Provisional ApplicationNo. 61/733,408, filed Dec. 4, 2012, entitled “SIP CLUSTER”, the entirecontent of which is incorporated herein by reference.

FIELD

This disclosure generally relates to software systems used in contactcenters and other enterprise communications systems, and moreparticularly to a modular, scalable, high availability system forhandling session initiation protocol (SIP) communications in a contactcenter.

BACKGROUND

Contact centers may be used by an organization to communicate in anefficient and systematic manner with outside parties. Such centers mayfor example have large numbers of agents staffing telephones, andinteracting with outside parties and with each other. Calls may beplaced on hold or into an interactive voice response (IVR) system whenfirst connected to the contact center; subsequently an agent may take acall, place it back on hold, transfer the call, conference in anotheragent, or take other such actions related to the call. Outside partiesmay also interact with a contact center by other mechanisms, includinginitiating contact through on-line chat, video, email, and the like.

The session initiation protocol (SIP) standard may be used in a contactcenter to conduct communications over an Internet Protocol (IP) network,which may operate within the contact center, and which may connect tooutside networks such as the public switched telephone network (PSTN)through one or more gateways. An IP network may also extend outside ofthe contact center, enabling, for example, communications with partiesconnected to the Internet without the need to use the PSTN.

It may in some situations be advantageous to construct large contactcenters, in which, for example, thousands of agents are employed. Alarge contact center may be helpful, for example, to an enterprise witha central contact telephone number from which each incoming call isdispatched to an agent according to the reason for the call, to anenterprise where it is often necessary to forward a call from one agentto another, or to an enterprise in which many agents work from differentgeographical locations. In such cases, it may be inefficient toconstruct multiple small independent call centers.

It may be advantageous for the software and hardware employed in a largecontact center to be modular, scalable, readily expanded or reduced insize, and suitable for providing high availability service. Scalabilitymay be important because performance-limiting bottlenecks may poseincreasingly difficult challenges as contact center deployments becomevery large.

SUMMARY

According to one aspect, a system for adding a new server, e.g., a SIPserver, to a cluster of servers, e.g., a SIP cluster, is provided. Stateinformation is transferred to the new server during the process.According to another aspect, a system for removing a server, e.g., a SIPserver, from a cluster of servers, e.g., a SIP cluster, is provided.State information is transferred from the server being removed, to theremaining servers, during the process.

According to an embodiment of the present invention there is provided amethod for adding a first server to a group of existing second serversassociated with a contact center, the method including: sending by thefirst server a request for initiating addition of the first server tothe group of existing second servers; sending, by each of the pluralityof existing second servers, in response to the request, stateinformation for a resource mapped to the existing second server, thestate information being transmitted to the first server without sendingthe state information to one of the existing second servers; andsending, by the first server, a commit message to each of the existingservers, in response to receiving the state information from each of theplurality of existing second servers; and changing the mapping of one ofthe resources from one of the existing second servers to the firstserver in response to the commit message.

In one embodiment, the method includes: sending, by the first server, toeach of the plurality of existing second servers, an initiate message;sending, by each of the plurality of existing second servers, to thefirst server, an initiation acknowledge message; and sending, by thefirst server, to each of the plurality of existing second servers, astate transfer request.

In one embodiment, the method includes: notifying a configurationserver, responsible for maintaining a list of servers, of the additionof the first server; updating, by the configuration server, the list ofservers; and notifying, by the configuration server, a set ofsubscribers of the update to the list of servers.

In one embodiment, the method includes: receiving a request associatedwith a resource mapped to the first server from the existing secondservers; identifying the first server as responsible for the resource;and routing the request to the first server in response to theidentifying.

In one embodiment, the identifying of the first server as responsiblefor the resource includes: providing, to a function, a resourceidentifier (ID) identifying the resource; and receiving as an outputfrom the function a module identifier (ID) for the first server.

In one embodiment, the function is a hash function.

In one embodiment, the hash function is a consistent hash function.

In one embodiment, the hash function includes: a first basic hashfunction configured to map resource identifiers into a range; and asecond basic hash function configured to map module identifiers into therange.

In one embodiment, the second basic hash function is further configuredto map a replica of each module identifier into the range.

In one embodiment, the hash function is configured to map resourceidentifiers corresponding to resources in a geographic region intomodule identifiers corresponding to servers executing on computingdevices in the geographic region.

According to an embodiment of the present invention there is provided amethod for removing a first server from a group of servers associatedwith a contact center, the group of servers including the first serverand a plurality of other second servers, the method including: sendingby the first server a request for initiating removal of the first serverfrom the group of servers; sending, by the first server, stateinformation for a resource mapped to the first server, the stateinformation being transmitted by the first server without stateinformation being transmitted by one of the other second servers; andsending, by the first server, a commit message to each of the othersecond servers; and changing the mapping of one of the resource from thefirst server to one of the other second servers to the first server inresponse to the commit message.

In one embodiment, the method includes: sending, by each of theplurality of other second servers, to the first server, an initiationacknowledge message.

In one embodiment, the method includes: notifying a configurationserver, responsible for maintaining a list of servers, of the removal ofthe first server; updating, by the configuration server, the list ofservers; and notifying, by the configuration server, a set ofsubscribers of the update to the list of servers.

In one embodiment, the method includes: receiving a request associatedwith a resource mapped to a remaining server of the plurality of othersecond servers from the first server; identifying the remaining serveras responsible for the resource; and routing the request to theremaining server in response to the identifying.

In one embodiment, the identifying of the remaining server asresponsible for the resource includes: providing, to a function, aresource identifier (ID) identifying the resource; and receiving as anoutput from the function a module identifier (ID) for the remainingserver.

In one embodiment, the function is a hash function.

In one embodiment, the hash function is a consistent hash function.

In one embodiment, the hash function includes: a first basic hashfunction configured to map resource identifiers into a range; and asecond basic hash function configured to map module identifiers into therange.

In one embodiment, the second basic hash function is further configuredto map a replica of each module identifier into the range.

In one embodiment, the hash function is configured to map resourceidentifiers corresponding to resources in a geographic region intomodule identifiers corresponding to servers executing on computingdevices in the geographic region.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome appreciated as the same become better understood with referenceto the specification, claims and appended drawings wherein:

FIG. 1 is a schematic diagram of layers of servers and agent devicesinterfacing to a SIP cluster according to an exemplary embodiment of thepresent invention;

FIG. 2 is a schematic diagram of data centers and contact centersaccording to an exemplary embodiment of the present invention;

FIG. 3 is a schematic diagram showing exemplary server modules in acontact center according to an exemplary embodiment of the presentinvention;

FIG. 4 is a schematic diagram of several SIP servers in a SIP cluster,interfacing with a feature server layer and a SIP proxy layer, accordingto an exemplary embodiment of the present invention;

FIG. 5A is a diagram of the mapping of SIP servers and DNs into acircular range to implement a consistent hash function according to anexemplary embodiment of the present invention;

FIG. 5B is a version of the diagram of FIG. 5A with a SIP serverremoved, according to an exemplary embodiment of the present invention;

FIG. 5C is a version of the diagram of FIG. 5A with replicas mapped intothe circular range for the SIP servers, according to an exemplaryembodiment of the present invention;

FIG. 6 is a message sequence diagram showing acts involved in adding aSIP server to a SIP cluster according to an exemplary embodiment of thepresent invention;

FIG. 7 is a message sequence diagram showing acts involved in removing aSIP server from a SIP cluster according to an exemplary embodiment ofthe present invention;

FIG. 8 is a message sequence diagram showing acts involved in respondingto a failed attempt to add two SIP servers to a SIP cluster according toan exemplary embodiment of the present invention;

FIG. 9 is a schematic diagram of modules participating in agentreservation for an incoming call according to an exemplary embodiment ofthe present invention;

FIG. 10 is a flow chart showing acts involved in agent reservationaccording to an exemplary embodiment of the present invention;

FIG. 11 is a flow chart showing acts involved in event deliveryaccording to an exemplary embodiment of the present invention;

FIG. 12 is a block diagram showing modules and components involved inthe generation and analysis of log files according to an exemplaryembodiment of the present invention;

FIG. 13 is a flow chart showing acts involved in the generation andanalysis of log files according to an exemplary embodiment of thepresent invention;

FIG. 14 is a schematic diagram of data centers and agent sites connectedby multiple networks according to an exemplary embodiment of the presentinvention; and

FIG. 15 is a schematic diagram of calling profiles and call categoriesaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of a SIPcluster provided in accordance with the present invention and is notintended to represent the only forms in which the present invention maybe constructed or utilized. The description sets forth the features ofthe present invention in connection with the illustrated embodiments. Itis to be understood, however, that the same or equivalent functions andstructures may be accomplished by different embodiments that are alsointended to be encompassed within the spirit and scope of the invention.As denoted elsewhere herein, like element numbers are intended toindicate like elements or features.

FIG. 1 is a schematic diagram of layers of servers and agent devicesinterfacing to a SIP cluster in a system supporting a contact centeraccording to one exemplary embodiment of the invention. The contactcenter may be an in-house facility to a business or corporation forserving the enterprise in performing the functions of sales and servicerelative to the products and services available through the enterprise.In another exemplary embodiment, the contact center may be a third-partyservice provider. The contact center may be hosted in equipmentdedicated to the enterprise or third-party service provider, and/orhosted in a remote computing environment such as, for example, a privateor public cloud environment with infrastructure for supporting multiplecontact centers for multiple enterprises.

According to one exemplary embodiment, the contact center includesresources (e.g. personnel, computers, and telecommunication equipment)to enable delivery of services via telephone or other communicationmechanisms. Such services may vary depending on the type of contactcenter, and may range from customer service to help desk, emergencyresponse, telemarketing, order taking, and the like.

In an exemplary embodiment, a contact center may include a number ofagent devices 338, each suitable for being operated by an agent, andeach connected to servers in the contact center. A cluster of sessioninitiation protocol servers (SIP servers), which may be referred to as aSIP cluster 105, may provide an interface layer to the agent devices338, and other contact center modules may interface with the SIP serverlayer by making requests and receiving responses according to aninterface which may be referred to as a T-library, TLib, or T-Lib. Otherinterfaces may also be used for communication between the modules in thecontact center, including SIP and sockets, which may be used to exchangeevents. For example, one or more statistics servers or stat servers 322may be employed to aggregate and maintain information about such dynamicdata as agent availability; these stat servers 322 may query the SIPcluster 105 for relevant data, and make it available to clients. Such aclient may be a graphical user interface operated by a contact centersupervisor monitoring the operation of the contact center. A reportinglayer, including one or more instances of an interaction concentrator120 (ICON 120), may also monitor the SIP server layer and captureinformation about calls arriving at the contact center, and store themfor subsequent analysis or troubleshooting. Other clients 125 mayinteract with both the SIP cluster 105 and the stat servers 322 toprovide management, troubleshooting, or reporting functions, or thelike.

FIG. 2 illustrates a geographically distributed contact center accordingto an exemplary embodiment, with a physical presence in multiplegeographic locations, which may be distributed over multiple countries.Some locations, which may be referred to as data centers 200, mayinclude equipment, such as computers, data storage equipment, andconnectivity equipment, along with one or more external communicationsconnections to networks outside of the data centers 200, such as thepublic switched telephone network (PSTN) or the Internet. Otherlocations, which may be referred to as agent sites 210, may includeequipment, such as computers, data storage equipment, and connectivityequipment, and also agent devices 338 (FIG. 3) and facilities allowinghuman agents to work within the agent sites 210 and use the agentdevices 338. The extent to which an agent site 210 hosts hardware maydepend on the nature and size of the facility and on the number ofagents the agent site 210 is intended to accommodate. A large agent site210 may host considerable computing, storage, and networking resources;a home agent site, e.g., the home of an agent working from home, maycontain a SIP phone or a SIP phone and a computer, or, if the externalcommunication connection is a PSTN connection, a computer runningtelephony software using a Telephony Application Programming Interface(TAPI) layer. The SIP cluster 105 may span the contact center, with SIPservers 318 (FIG. 3), e.g., instances of the SIP server process, runningon machines in several, or all, of the geographic locations. The SIPservers 318 of the SIP cluster 105 may be in communication with eachother.

FIG. 3 illustrates an exemplary embodiment of an agent site 210, whichmay be a contact center or part of a larger contact center, customers,potential customers, or other end users (collectively referred to as endusers) desiring to receive services from the contact center may initiateinbound calls to the contact center via their end user devices 310 a-310c (collectively referenced as 310). Each of the end user devices 310 maybe a communication device conventional in the art, such as, for example,a telephone, wireless phone, smart phone, personal computer, electronictablet, and/or the like. The mechanisms of contact in a call, and thecorresponding user devices 310, need not be limited to real-time voicecommunications as in a traditional telephone call, but may be non-voicecommunications including text, video, and the like, and may includeemail or other non-real-time means of communication. Thus the term“call” as used herein is not limited to a traditional telephone call butis a generalized term including any form of communication in which acontact center may participate.

Inbound and outbound calls from and to the end user devices 310 maytraverse a telephone, cellular, and/or data communication network 314depending on the type of device that is being used. For example, thecommunications network 314 may include a private or public switchedtelephone network (PSTN), local area network (LAN), private wide areanetwork (WAN), and/or public wide area network such as, for example, theInternet. The communications network 314 may also include a wirelesscarrier network including a code division multiple access (CDMA)network, global system for mobile communications (GSM) network, and/orany 3G or 4G network conventional in the art.

According to one exemplary embodiment, the contact center includes agateway 312 coupled to the communications network 314 for receiving andtransmitting calls and/or data between end users and the contact center.The gateway 312 may provide an interface between the internal network ofthe contact center and one or more external networks.

The contact center may also include a multimedia/social media server324, which may also be referred to as an interaction server, forengaging in media interactions other than voice interactions with theend user devices 310 and/or web servers 332. The media interactions maybe related, for example, to email, chat, text-messaging, web, socialmedia, and the like. The web servers 332 may include, for example,social interaction site hosts for a variety of known social interactionsites to which an end user may subscribe, such as, for example,Facebook, Twitter, and the like. The web servers may also provide webpages for the enterprise that is being supported by the contact center.End users may browse the web pages and get information about theenterprise's products and services. The web pages may also provide amechanism for contacting the contact center, via, for example, web chat,voice call, email, web real time communication (WebRTC), or the like.Although in FIG. 3 only one instance of each of the servers is shown, acontact center may contain multiple instances of any server, and it maybe advantageous to operate multiple instances for load sharing and toimprove performance.

According to one exemplary embodiment of the invention, the gateway 312is coupled to an interactive voice response (IVR) server 334. IVR is atechnology that allows a computer to interact with humans through theuse of voice and dual-tone multi-frequency (DTMF) tones input viakeypad. In telecommunications, IVR allows customers to interact with acontact center via a telephone keypad or by speech recognition, afterwhich they can service their own inquiries by following the IVRdialogue. IVR systems can respond with prerecorded or dynamicallygenerated audio to further direct users on how to proceed. IVRapplications can be used to control almost any function where theinterface can be broken down into a series of simple interactions. Inone exemplary embodiment, the IVR server 334 is configured, for example,with an IVR script for querying customers on their needs. The IVR server334 is configured, for example, with an IVR script for queryingcustomers on their needs. For example, a contact center for a bank maytell callers, via the IVR script, to “press 1” if they wish to get anaccount balance. If this is the case, through continued interaction withthe IVR, customers may complete service without needing to speak with anagent.

Once an appropriate agent is available to handle a call, the call istransferred to the corresponding agent device 338 a-338 d (collectivelyreferenced as 338). An agent device may be a telephone or it may be acomputer with an attached display, such as agent device 338 c, which maybe referred to as an agent desktop. Collected information about thecaller and/or the caller's historical information may also be providedto the agent device for aiding the agent in better servicing the call.In this regard, each agent device 338 may include a telephone adaptedfor regular telephone calls, VoIP calls, and the like. The agent device338 may also include a computer for communicating with one or moreservers of the contact center and performing data processing associatedwith contact center operations. The selection of an appropriate agentfor routing an inbound call may be based, for example, on a routingstrategy employed by the routing server 320, and further based oninformation about agent availability, skills, and other routingparameters provided, for example, by a statistics server 322, which mayalso be referred to as a stat server 322. A SIP server 318 provides aninterface to agent devices 338.

The multimedia/social media server 324 may also be configured toprovide, to an end user, a mobile application 340 for downloading ontothe end user device 310. The mobile application 340 may provide userconfigurable settings that indicate, for example, whether the user isavailable, or not available, or the user's availability is unknown, forpurposes of being contacted by a contact center agent.

The contact center may also include a reporting server 328 configured togenerate reports from data aggregated by the stat server 322. Suchreports may include near real-time reports or historical reportsconcerning the state of resources, such as, for example, average waitingtime, abandonment rate, agent occupancy, and the like. The reports maybe generated automatically or in response to specific requests from arequestor (e.g. agent/administrator, contact center application, and/orthe like).

To store configuration information such as device characteristics andagent attributes, such as agent skill levels, a configuration server 342may be included in the system. The configuration server 342 may, forexample, provide attribute values for objects or processes when theseare created, at system startup, or subsequently. A feature server 425may provide various features within the contact center, such as voicemail and a dial plan, and a SIP proxy 346, which performs the functionsof a SIP element also known in the art as a SIP registrar.

According to one exemplary embodiment of the invention, the contactcenter also includes a mass storage device 330 for storing data relatedto contact center operations such as, for example, information relatedto agents, customers, customer interactions, and the like. The massstorage device may take the form of a hard disk or disk array as isconventional in the art.

Each of the various servers of FIG. 3 may be a process or thread,running on one or more processors, in one or more computing devices,executing computer program instructions and interacting with othersystem components for performing the various functionalities describedherein. The computer program instructions are stored in a memory whichmay be implemented in a computing device using a standard memory device,such as, for example, a random access memory (RAM). The computer programinstructions may also be stored in other non-transitory computerreadable media such as, for example, a CD-ROM, flash drive, or the like.Also, a person of skill in the art should recognize that a computingdevice may be implemented via firmware (e.g. an application-specificintegrated circuit), hardware, or a combination of software, firmware,and hardware. A person of skill in the art should also recognize thatthe functionality of various computing devices may be combined orintegrated into a single computing device, or the functionality of aparticular computing device may be distributed across one or more othercomputing devices without departing from the scope of the exemplaryembodiments of the present invention. A server may be a software module,which may also simply be referred to as a module. The set of modules inthe contact center may include servers, and other modules.

Each module may for example be a thread or a process. The modules in thecontact center may communicate by various means, including events andmessages. Two modules may be connected by a point-to-point socketconnection, and in this case either module may send events to the other.Messages may be sent by one module to another module via a messageserver 344, which also provides the ability to send a broadcast messageto multiple recipient modules simultaneously. Other messages known inthe art, and referred to herein, as SIP messages, may also be exchangedbetween the modules of the contact center and with entities external tothe contact center.

It may be advantageous for the software and hardware employed in acontact center to be modular, scalable, readily expanded or reduced insize, and suitable for providing high availability service. A modulardesign, using multiple copies of identical modules of different types,configured at startup or reconfigured at run-time, may be operated toprovide these advantages. The size of the deployment may be changed byincreasing or decreasing the number of modules executing, addingprocessors to the system if necessary. High availability may beprovided, for example, by mirroring state information between modules,so that several modules are in a position to perform any given task, sothat if one module fails, as a result of a software error or hardwarefailure, another module, operating on another processor if necessary,may perform the failed module's tasks. Scalability may be achieved bydesign practices which avoid bottlenecks in data flow or processingresources, e.g., design practices which avoid routing large volumes ofdata through a single central location.

FIG. 4 illustrates several SIP servers 318 forming a SIP cluster, alongwith a feature server layer and a SIP proxy layer 420, according to anexemplary embodiment. Each SIP server 318 may contain, or include,several modules, such as a session controller (SC) 405, an interactionproxy (IP) 410 and a T-controller (TC) 415, each of which may run as oneor more threads within the SIP server process. Two additional layers, aSIP proxy (SP) layer 420, and a layer of feature servers 425 (FS), mayprovide services for the SIP server 318. The SIP proxy layer 420 maycontain, for example, instances of the SIP proxy 346.

Each agent device may be associated with one or more directory numbers(DNs). A DN may be an identifier for a network endpoint at a userinterface. A telephone may, for example, have a DN corresponding to itsphone number, or it may have multiple DNs if it supports multiple lines,each of which may be a DN. Other DNs may be implemented in an IVR, or ina session controller 405 (where the DN may be known as a route point)for the purpose of providing a temporary hold location for a call. Othertypes of identifiers used with other user interfaces, such as an emailaddress, or a login identity for chat, may also be DNs. In the SIPserver 318, each T-controller 415 may own, for example by overseeing orbeing responsible for, multiple agent device DNs, where ownership inthis context implies a many-to-one relationship: in this case aT-controller 415 may own many agent device DNs and each agent device DNmay have one owner.

I. Dynamic Changes in SIP Cluster Size

In operation, it may on occasion be advantageous to remove a SIP server318 from the SIP cluster 105, or to add a SIP server 318 to the cluster.For example, if a computing device on which a SIP server 318 executesrequires service, the SIP server 318 may be removed from the SIP cluster105, and the computing device may be shut down. The computing device maybe replaced with another computing device, on which a new instance ofthe SIP server 318 may be started, and the new SIP server may be addedto the SIP cluster 105. It may be advantageous to be able to performthese operations with as little disruption as possible.

Each SIP server instance may contain a T-controller 415 which may ownmultiple DNs, and which may maintain state information for the DNs itowns. A T-controller may own many DNs, e.g., 4,000 DNs, and the totalnumber of DNs in the contact center may be significantly larger still.It may be advantageous for a module in the contact center initiating aninteraction with a DN to identify the T-controller owning the DN. Itmay, however, be costly to maintain a complete record of DN ownership ineach such module, because of the potentially large volume of datainvolved, and the cost of keeping this data current as the contactcenter changes dynamically, e.g., as SIP servers 318 or DNs are added orremoved. Moreover, any solution involving centralized storage of acomplete record of DN ownership may result in a data flow or processingbottleneck. To reduce the effect of these drawbacks, a hash function maybe used to map the set of DNs onto the set of SIP servers 318 and,thereby, to the set of T-controllers owning the respective DNs.

It may be advantageous for the hash function to have properties thatresult in the least disruption possible when a SIP server 318 is addedor removed. When a SIP server 318 is added or removed, some DNspreviously mapped, by the hash function, to other SIP servers 318, maybecome mapped to the new SIP server; conversely when a SIP server 318 isremoved, the DNs mapped to the SIP server being removed may becomemapped to other SIP servers 318. It may be advantageous for the newownership mapping to result in the smallest number of DNs changingowners. For example, it may be advantageous for a change in ownership tooccur for the DNs assigned to a SIP server that is being removed, or forDNs which are being transferred to a SIP server which is being added.

The hash function used to identify the DN owners may map the set of DNsonto the set of SIP servers. Because the set of SIP servers may changewhen a SIP server 318 is added or removed, a set of SIP serveridentifiers, e.g., unique identifiers assigned to each SIP server 318,may be an input when the hash function is executed. The identifier ofthe DN being mapped to an owner may also be an input to the hashfunction. The output of the hash function may be the identifier of theSIP server which owns the DN, through the T-controller executing in theSIP server.

In one exemplary embodiment, when a SIP server 318 is removed from theSIP cluster 105, it transfers its state information and itsresponsibilities, such as DN ownership, to another SIP server 318, sothat the operation, e.g., of the DNs owned by the SIP server beingremoved from the cluster, may continue without interruption.

In one embodiment, consistent hashing may be used to provide a hashfunction to map each DN to its owner SIP server, in a manner thatresults in little disruption when a SIP server 318 is added or removed.FIG. 5A shows a layout diagram illustrating a mapping, by a consistenthash function, of six DNs to three SIP servers, and FIG. 5B shows alayout diagram illustrating a mapping, by the same consistent hashfunction, of six DNs to two SIP servers. A consistent hash functionwhich maps the domain of DN identifiers into the range of SIP serveridentifiers may be constructed using a first basic hash function, whichneed not be a consistent hash function, to map the DN identifiers to aninterim range, which may be a range of integers. A second basic hashfunction, which may be the same hash function as the first basic hashfunction, having the same range, may be used to map the SIP serversidentifiers to the same interim range. The interim range may be mappedto a circle, and the consistent hash function is the mapping thatresults when the DN is mapped to the nearest SIP server hash point, whenproceeding in a clockwise direction on the circle. In the exampledepicted in FIG. 5A, in an initial state a first DN 805 and a second DN810 are mapped to a first SIP server 815; a third DN 820, a fourth DN825 and a fifth DN 830 are mapped to a second SIP server 835; and asixth DN 840 is mapped to a third SIP server 845. If the second SIPserver 835 is removed (FIG. 5B), the first DN 805 and the second DN 810remain mapped to the first SIP server 815, because it remains thenearest point to them on the circle in a clockwise direction. After theremoval of the second SIP server 835, the third DN 820, the fourth DN825 and the fifth DN 830 are mapped to the third SIP server. The sixthDN 840 remains mapped to the third SIP server 845. In this example, theDNs which move to a different owner, e.g., SIP server, as a result ofthe removal of the second SIP server 835 are the third DN 820, thefourth DN 825 and the fifth DN 830, which could not remain mapped to thesecond SIP server 835 after the second SIP server 835 was removed. Inthis example, none of the DNs mapped to the first SIP server 815 aremoved to the third SIP server 845, nor vice versa, as a result of theremoval of the second SIP server 835.

Similarly, if the initial state were the one of FIG. 5B, with two SIPservers, the first SIP server 815 and the third SIP server 845, and thefinal state the one of FIG. 5A, with three SIP servers, then theaddition of one SIP server, the second SIP server 835, would againresult in the reassignment of three DNs, the third DN 820, the fourth DN825 and the fifth DN 830, which would be moved to the newly added secondSIP server 835.

The uniformity of the distribution of DNs across SIP servers may beimproved by hashing one or more replicas of each SIP server identifierinto the range, e.g., onto the circle. This may be done, for example,for each SIP server, one at a time, by executing one of the basic hashfunctions, or another hash function having the same range, repeatedly,each time using as input the output of the last execution of the hashfunction. Each new output forms an additional replica in the range. Inthis example, a DN may be mapped to a SIP server 318 when the SIP serveridentifier or one of its replicas is the nearest point on the circle ina clockwise direction, to the hash of the DN identifier. FIG. 5C shows alayout diagram of a mapping formed using replicas of SIP serveridentifiers, according to an exemplary embodiment. If replicas 850, 855of the first SIP server 815, replicas 860, 865 of the second SIP server835, and replicas 870, 875 of the third SIP server 845 are added, thenthe consistent hash function will map the third DN 820 and the fourth DN825 to the first SIP server 815 through its replica 850, the first DN805 and the fifth DN 830 to the second SIP server 835 (the formerthrough the replica 860) and the second DN 810 and the sixth DN 840 tothe third SIP server 845 (the former through the replica 870), e.g., twoDNs are mapped to each SIP server. The use of replicas and the resultingimproved uniformity of the distribution of DNs across SIP servers maymean that the number of DNs owned by the various SIP servers is morenearly the same than in the absence of the use of replicas, in whichcase some SIP servers may own few DNs and some may own many. Althoughparticular numbers of SIP servers and DNs have been used for purposes ofillustration in these examples, the invention is not limited thereto,and may be used with different numbers of SIP servers and DNs.

Consistent hashing is discussed in Karger, D.; Lehman, E.; Leighton, T.;Panigrahy, R.; Levine, M.; Lewin, D. (1997) “Consistent Hashing andRandom Trees: Distributed Caching Protocols for Relieving Hot Spots onthe World Wide Web,” Proceedings of the Twenty-ninth Annual ACMSymposium on Theory of Computing, the contents of which are incorporatedherein by reference.

It should be apparent to one of skill in the art that the invention isnot limited to the consistent hash described in this example, and thatthe interim range, for example, may be a range of floating pointnumbers, for example, or a range of string values. It should also beapparent that the mapping of the interim range to a circle is aconceptual device for illustrating a mapping to a range with a wrappingcharacteristic, so that the last element in the range is defined to beadjacent to the first. The DNs may equally well be mapped to the nearestSIP server in a counterclockwise direction, instead of in a clockwisedirection. The hash function need not be a consistent hash function butmay be any other hash function with, or without, the characteristic ofproducing minimal disruption, e.g., minimal re-mapping of owned objects,e.g., DNs, to owners, e.g., SIP servers or T-controllers, when the setof owners is changed.

If a contact center is geographically distributed, it may beadvantageous to have SIP server instances located near, e.g., in thesame country as, the DNs they own, through their T-controllers. This maybe accomplished by defining a different consistent hash function foreach geographic region. For example, to determine the owner of a DN incountry A, the consistent hash function may be executed with inputincluding SIP server identifiers corresponding to SIP servers executingon computing devices in country A.

FIG. 6 is a message sequence diagram illustrating the addition of a SIPserver to a SIP cluster according to an exemplary embodiment. Theaddition of a SIP server to a SIP cluster may proceed in several acts.In act 905, a SIP server 901 to be added, may send an initiate messageto each of the existing SIP servers 902, notifying them that the processof adding a new SIP server 901 has been initiated. Each of the existingSIP servers 902 may, in act 910, respond with an initiation acknowledgemessage. In act 915, the new SIP server 901 may send a state transferrequest to the existing SIP servers 902. The existing SIP servers 902may, in act 920, respond by transferring, to the new SIP server 901,state information for any DNs being moved, as determined by the hashfunction, which may be executed with a list of SIP servers including thenew SIP server 901. Such state information may include the status of theDN, e.g., whether the DN is on hook, off hook, whether a call is beingdialed from the DN, or whether the DN is in an after call work state,which may be used when an agent is performing post-interaction workafter completing a call. The new SIP server 901 may, in act 935, send acommit message to each existing SIP server to finalize the new SIPcluster configuration, which then may include the new SIP server 901. Inthe interval between receipt of the initiate message and the receipt ofthe commit message, the existing SIP servers may stop processing events,e.g., place all events related to the affected DNs on hold. The commitmessage may notify the other SIP servers that the process of adding thenew SIP server has been finalized and that the other SIP servers are nolonger responsible for the DNs which have been moved, and that they maydelete the state information for these DNs. Although the acts aredescribed in a particular order in this example, the invention is notlimited to acts occurring in this order, and some or all of the acts maytake place in a different order, or in parallel.

FIG. 7 is a message sequence diagram illustrating the removal of a SIPserver from a SIP cluster according to an exemplary embodiment. When aSIP server 1001 is to be removed from a SIP cluster, it may transfer thestate information in its possession to the other SIP servers 1002 in theSIP cluster. In act 1005, the SIP server 1001 being removed may send aninitiate message to each of the other SIP servers 1002, notifying themthat the process of removing the SIP server being removed has beeninitiated. Each of the other SIP servers 1002 may, in act 1010, respondwith an initiation acknowledge message. The SIP server being removedmay, in act 1015, transfer its state information to the other SIPservers, transferring state information for each DN to the SIP serverwhich will become the owner of the DN. The new owner for each DN isidentified by the hash function, which is executed with a list of SIPservers excluding the SIP server 1001 being removed. Each of the otherSIP servers 1002 may, in act 1020, send a state information acknowledgemessage, acknowledging that it has received the state information, andin act 1025, the SIP server being removed may send a commit message. TheSIP server being removed may stop processing events when it sends theinitiate message. The other SIP servers may stop processing events,e.g., place all events related to the affected DNs on hold, in theinterval between the initiate message and the receipt of the commitmessage. The commit message may notify the other SIP servers that theprocess of removing the SIP server 1001 being removed has been finalizedand that the other SIP servers have become responsible for the DNs, andfor maintaining state information for the DNs. Although the acts aredescribed in a particular order in this example, the invention is notlimited to acts occurring in this order, and some or all of the acts maytake place in a different order, or in parallel.

FIG. 8 is a message sequence diagram illustrating recovery from anunsuccessful attempt to add two SIP servers to a SIP cluster accordingto an exemplary embodiment. An attempt to add a SIP server 1101 may beunsuccessful if there is an attempt to add another SIP server 1102 atnearly the same time. For example a first new SIP server 1101 may send,in act 1105, a first initiate message to the existing SIP servers 1103,1104, and the second new SIP server 1102 may send, in act 1110, a secondinitiate message to the existing SIP servers 1103, 1104. A firstexisting SIP server 1103 may receive the first initiate message first,whereas a second existing SIP server 1104 may receive the secondinitiate message first. In this case the first existing SIP server 1103may reply with an acknowledge message to the first new SIP server 1101and with an error message to the second new SIP server 1102, and thesecond new SIP server 1104 may reply with an acknowledge message to thesecond new SIP 1102 server and with an error message to the first newSIP server 1101. Each of the new SIP servers 1103, 1104, having receivedan error message in reply to an initiate message, may send an abortmessage 1120, 1125 to the existing SIP servers, terminating the attemptto add the new SIP servers. The SIP servers being added may each start anew attempt to join the SIP cluster, after waiting a random amount oftime. Although the acts are described in a particular order in thisexample, the invention is not limited to acts occurring in this order,and some or all of the acts may take place in a different order, or inparallel.

Because a list of SIP servers may be input to the consistent hashfunction, any module that will execute this hash function may maintain alist of SIP servers. When a SIP server is added to or removed from thecluster, the configuration server, which may keep a list of SIP servers,may be notified. It may send out an update notification, announcing thechange, in the form of a message or an event, to each module whichpreviously registered to receive updates on the list of SIP servers.This avoids the need for each module to obtain an updated list of SIPservers from a central location, such as the configuration server, everytime the consistent hash function is to be executed.

II. Agent Reservation in a Distributed System

When a call arrives at a contact center, information about the call andthe caller may be gathered, such as the caller's history with thecontact center and the purpose of the call. A target agent, e.g., anagent appropriate for handling the call, may be identified by a module,and it may be advantageous to route the call to a DN at which the targetagent can be reached. To do so, it may be advantageous to identify amodule which owns the DN, e.g., a T-controller which owns the DN, or aSIP server which contains the T-controller which owns the DN. Thisidentification may be performed using the hash function which maps DNsto SIP servers.

FIG. 9 shows several modules which may, in one exemplary embodiment,participate in the handling and routing of a call. When a call arrivesat the contact center, it is handled by the SIP proxy layer, whichassigns it to a first session controller 510. The assignment may be madein a manner which balances, as nearly as possible, the load on thesession controllers 405, using, for example, a round-robin algorithm.The first session controller 510 is part of, for example, via a threadexecuting within, a first SIP server 515. Once assigned to the firstsession controller 510, the call is initially placed on a route point inthe first session controller 510, such as, for example, on a DN in thefirst session controller 510, for temporarily holding the call. Therouting server (URS) 320 may have subscribed to a list of availableagents meeting certain criteria, provided by a stat server 322 (FIG. 3).The criteria may include, for example, certain combinations of skills.When an agent meeting the required criteria becomes available, orunavailable, the stat server may send a notification to the routingserver 320, identifying the agent and the agent's DN, e.g., a DN towhich the agent is logged in, and specifying whether the agent hasbecome available or unavailable. This may allow the routing server 320to maintain a current list of available agents meeting the criteria andtheir respective DNs. When the call arrives at the route point in thefirst session controller 510, the session controller may send an event,which may include call data, to various clients including the routingserver 320, informing them of the arrival of the call. Upon receipt ofthis event, the routing server may use the call data, which may includeIVR responses identifying, for example, a product of interest, to selecta suitable agent from the list of available agents, e.g., an agentfamiliar with the product. Thus, when the routing server 320 selects atarget agent and DN to which to attempt to route the call, the computingdevice on which the routing server 320 executes identifies a resource(e.g., an agent and a DN) appropriate for handling the call.

In an embodiment that may be referred to as involving implicit agentreservation, once the routing server 320 selects a target DN 530 towhich to route a call, the routing server 320 sends to the first sessioncontroller 510 (“Session Controller 2” in FIG. 9) a routing request withan embedded implicit agent reservation request, instructing the firstsession controller 510 to attempt to route the call to the target DN 530(“DN 1” in FIG. 9). The target DN 530 may be owned by a T-controller525, in a SIP server 535, but the first session controller 510 may lackinformation about the location of the target DN 530, e.g., it may havereceived, in the routing request, an identifier for the target DN 530,but it may lack an identifier for the T-controller which owns the targetDN 530, or for the SIP server which contains this T-controller.According to one embodiment, identification of the SIP server 535responsible for the target DN 530 is based on the hash function, whichmay be executed by the first session controller 510 assigned to thecall. According to one embodiment, the hash function maps an input DN toa unique identifier for the SIP server 535 containing the T-controller525 which owns the input DN, e.g., the target DN 530.

In the illustrated example, the first session controller 510 isconfigured to execute the hash function using as input the target DN530, identified by the routing server, and to identify, based on thehash function, the second session controller 520 which, according to theexample, owns the target DN 530. Once the owner is identified, the firstsession controller 510 transmits an agent reservation request to thesecond session controller 520. In another embodiment, the T-controllersmay instead perform some of these functions: the first sessioncontroller 510 sends the agent reservation request to a T-controller 505which is in the same SIP server 515 as the first session controller 510.The T-controller 505 is configured to execute the hash function using asinput the target DN 530, identified by the routing server 320, and toidentify, based on the hash function, the T-controller 525 which,according to this embodiment, owns the target DN 530. Once the owner isidentified, the T-controller 505 transmits an agent reservation requestto the T-controller 525 which owns the target DN 530.

In the illustrated example, the T-controller 525 executing in the secondSIP server 535 receives the agent reservation request, and accordingly,the computing device within which the T-controller 525 executes receivesthe request. In the terminology used herein, the computing device issaid to receive the request whether the request originated from a threador process executing in a different computing device or in the samecomputing device.

When the T-controller 525 receives the agent reservation request, it mayrespond with a message granting the reservation, or denying it. If therequest is granted, the first session controller 510 may transfer thecall to the agent's DN 530; if the request is denied, the first sessioncontroller 510 may notify the routing server 320 which then may make arenewed request to the stat server 322, for an alternate agent to handlethe call.

FIG. 10 is a flow diagram of a process for distributed agent reservationaccording to one embodiment. In act 610, a routing server 320, executingon a computing device, identifies a resource, e.g., an agent,appropriate for handling a call held by the first session controller510, and sends this information to the first session controller 510. Inact 620, the first session controller 510 executes a hash function toidentify the SIP server responsible for the resource, and, in act 630,the first session controller 510 sends an agent reservation request tothe T-controller in the identified SIP server. The T-controller, in act640, receives the request. In an act 645, the T-controller performsreservation arbitration as described below, and in act 650, determineswhether to grant or deny the request. In one embodiment, the reservationarbitration is performed by an agent reservation module in theT-controller. If the request is granted, the first session controller510 routes the call in act 660; otherwise, the process starts again withthe routing server 320 identifying an alternate resource. As explainedabove, in one embodiment some of the acts, such as the execution of thehash function, are performed by another module, e.g., a T-controller.Although the acts are described in a particular order in this example,the invention is not limited to acts occurring in this order, and someor all of the acts may take place in a different order, or in parallel.

If the DN is already reserved, e.g., if another routing server hasalready sent an agent reservation request which has been granted, theT-controller may deny the agent reservation request. If the T-controller525 has not yet granted an agent reservation request, the T-controller525 may use an arbitration process to determine whether to grant or denythe request. In one exemplary embodiment, the T-controller 525 waits forsome interval of time, for other agent reservation requestscorresponding to other calls to arrive, and grants the agent reservationrequest having, for example, the highest priority, and denies theothers. If several agent reservation requests have the same priority itmay select, at random, one to be granted, and deny the others. Thepriority of an agent reservation request may be evaluated by the routingserver 320, using an algorithm that takes into account various criteria,including, for example, a characteristic of the caller such as the valueof the caller, e.g., whether the caller is expected to be a significantsource of income to the enterprise, the hold time, e.g., the length oftime the caller has already been waiting to speak with an agent, thesuitability of the agent for the call, and/or the suitability of otheragents for the call. For example, the request may be given higherpriority if the caller needs help with a particular product and theagent is one of few agents at the contact center familiar with thatproduct. The routing server then may send an assessment of the priorityof the call along with the agent reservation request. In one embodiment,the reservation arbitration is performed by an agent reservation modulein the T-controller.

Routing servers 320 may communicate with each other about call routingand/or agent selections as they are made, reducing the likelihood thattwo routers 320 will attempt to route different calls to the same agent.This mechanism is not foolproof, however, in part because the routingservers 320 may execute on different computing devices, resulting incommunication delays. The agent reservation module acts as a centralarbiter for the agent and the DN, making it possible for multiplerouting servers 320 to obtain a reliable response granting or denying anagent reservation request.

In one exemplary embodiment, the first session controller 510 may makean explicit agent reservation request by sending an agent reservationrequest not embedded in a routing request to the first sessioncontroller 510. The second session controller 510 may execute the hashfunction to identify the second session controller 520, send the agentreservation request to the second session controller 520, and, whetheror not the agent reservation request is granted, send a response to therouting server 320 indicating whether the agent reservation request wasgranted. If the agent reservation request is granted, the router thensends a route request to the first session controller 510, which routesthe call to the T-controller 525 which owns the target DN 530.

Although in the examples described here the agent is associated with asingle DN, the invention is not limited to this case, and thereservation logic may be expanded to include configurations in which anagent may be logged in to, or otherwise associated with, more than oneDN.

A modular approach such as that of the present invention providesseveral benefits, including scalability, e.g., the ability to expand thesize of an implementation without being constrained by performancebottlenecks, and resilience, e.g., the ability of the system to adjustquickly and without disruption to the failure of an element.

III. Delivery of Events to Agents in a Distributed System

If the agent reservation request is granted, the first sessioncontroller 510 may, in addition to routing the call to the target DN530, generate an event, such as a ringing event for causing the targetDN 530 to ring, or a screen pop event for causing information related tothe call to be made available to the agent, for example in the form of ascreen pop. This event, like the agent reservation request, is to berouted to the T-controller which owns the agent device on which thescreen pop is to appear. The T-controller may be the same T-controlleras the T-controller 525 which owns the target DN 530: in one exemplaryembodiment, for example, the agent device is an integrated devicecontaining display features and telephony capabilities, and the agentdevice has a single DN. To route the screen pop event to the targetdevice, the first session controller 510 executes the hash function,passing in the DN as an argument and receiving as output an identifier,e.g., a unique string, identifying the SIP server containing theT-controller 525 which owns the agent device. In this context, the agentdevice is another example of a resource. The first session controller510 then dispatches the event to the T-controller 525, which forwards itto the agent device, causing the agent device to respond to the event,e.g., providing output to the agent by generating a ringing alert inresponse to a ringing event, or by displaying a screen pop in responseto a screen pop event.

FIG. 11 is a flow diagram of a process for distributed event deliveryaccording to one embodiment. In act 710, a computing device in which thefirst session controller 510 executes generates an event, and thecomputing device, again through the execution of the first sessioncontroller 510, identifies the SIP server to which the event is to bedelivered, by, in act 720, executing a hash function. In act 730 thefirst session controller 510 sends the event to the T-controller in theSIP server to which the event is to be delivered, the T-controllerreceives the event, in act 740, and, in act 750, the agent devicegenerates output, such as a ringing alert, or a screen pop, for theagent. Although the acts are described in a particular order in thisexample, the invention is not limited to acts occurring in this order,and some or all of the acts may take place in a different order, or inparallel.

IV. Analysis of Log Files in a Distributed System

The threads executing in various modules in the contact center may, inoperation, generate records, which may be referred to as log files, ofaspects of their operation. For example, a thread may record, or log,each message or event it sends to another thread, or receives fromanother thread. During operation, each thread writes to a separate logfile. It may on occasion be advantageous to review or analyze such logfiles, to assess the performance of the contact center, or to diagnoseunusual or erroneous activity. Log files may be large, however, and forany particular investigation, some of the information in a log file maybe of little interest. Moreover, as modules interact, log entriesrelated to these interactions may be recorded in different log files. Atool for systematically identifying, classifying, and displayingrelevant information in log files may therefore be of use.

FIG. 12 is a block diagram of modules 415, 405, 1215 generating logfiles 1210, which are parsed by a log parser 1215 into a database 1220,queried by a client 1230 according to an exemplary embodiment. A logfile analysis tool may operate in two stages, a first stage referred toas a parsing stage, and a second stage referred to as a query stage.These stages may subsequently be repeated. In one embodiment, one ormore log files 1210 are written, during operation, by, e.g., aT-controller 415, a session controller 405, and a SIP proxy 1210. Logfiles may also be written by other types of module, including statservers 322, routing servers 320, or ICONs 120. At the beginning of theanalysis, the log files of interest are put into one directory, orfolder, accessible from a computer. In the parsing stage, one or more ofthe log files are read by a log parser 1215, and their contents arewritten to tables in a database 1220. The database 1220 may contain adedicated table for each thread. Certain fields, referred to as basicfields, may be present in each table in the database 1220; other fieldsmay be present in some tables and may not have meaningful values forsome threads. Examples of basic fields may include a time stamp for eachlog entry, the position of each log entry in the log file, and the filename of the log file.

Other basic fields may include, for T-Lib messages, the DN number andthe connection ID, a unique identifier for the connection, and, for SIPmessages, fields identified by names known to those of skill in the artas the following: Call-ID, CSeq, Message type, To URI, From URI, Via, RI(top most), Via branch, Request URI, Destination IP, Destination port,Source IP, and Source port.

In one exemplary embodiment, each thread is configured to record a logentry known as a trigger when it sends to another thread an event ormessage in response to which the receiving thread is expected to takesome action. The trigger includes a unique identifier, which is sent aspart of the message or event. The receiving thread then records, in itslog file, a log entry known as a handler when it begins handling, e.g.,responding to, the message or event, and another handler when itcompletes handling the message or event. Each handler log entry containsthe same unique identifier present in the trigger log entry, and the twohandlers provide starting and ending boundaries in the receivingthread's log file for log entries made while handling the message orevent. The unique identifier present in a trigger or handler message isalso a basic field in any database table for a thread which may recordtriggers or handlers.

For example, in an analysis session, the log files generated during atime interval may be collected in one directory. These log files mayinclude files generated by a SIP server 318, e.g., one log file for eachthread executing within the instance of SIP server, a log file for arouting server 320, a log file for a stat server 322, a log file for aSIP proxy 346, and a log file for a feature server 425. An analyst maywish to view activity involving a particular thread, such as a threadnamed TServer which executes in the session controller 405, which inturn is part of the SIP server process. The analyst may run the logparser, selecting the log file corresponding to the TServer thread, andthe log parser may be configured to transcribe each entry into thedatabase, parsing each entry to extract fields of interest, such as thebasic fields, and other fields identified by the parser for this type oflog file.

In a stage of querying the database using a client which may be referredto as a front end, the analyst may then, for example, perform a queryrequesting transactions related to a particular calling phone number,e.g., a phone number for which a connection problem was reported. Thefront end may include a user interface, suitable for receiving input,such as mouse clicks, from the user, and for displaying results to theuser. The query may reveal that a call from this number was received bythe TServer thread, but the call was not answered, e.g., the calltriggered a transaction at the SIP server layer but no result wastriggered.

The session controller 405 may contain two threads, a TServer thread anda call manager thread, and the latter may be responsible for SIPmessaging. To further investigate the cause of the unanswered call, theanalyst may invoke the log parser to parse the call manager thread's logfile, and perform queries, to display both T-Lib messages and SIPmessages, from both threads, in, for example, chronological order. Auser interface module may display the results of each query in auser-readable format. Because the log file name and the position in thelog file of each log entry are basic fields in each table in thedatabase 1220, the user interface may provide to the user the ability,by clicking on a data item displayed in the user interface, to open thelog file from which this data item was originally retrieved, and tohighlight the corresponding log entry in the log file. Using the logfile name and the position in the log file of each log entry, the querymay also display, e.g., in a separate adjacent pane or window next tothe query results, the log file entries from which these query resultsoriginated, and each such log file entry may be clickable, e.g.,clicking on it may cause a viewer to open, allowing the user to see theentire contents of the log file containing the entry, e.g., with theentry highlighted. For example, in the adjacent pane or window, thefront end may display a series of log file entries in chronologicalorder, showing, e.g., the log file entry corresponding to the sending ofa message from one module, followed by the log file entry, from adifferent log file, corresponding to the receipt of the message byanother module, and followed by log file messages corresponding to actsexecuted by the second module in handling the message.

FIG. 13 is a flow chart illustrating acts involved in log file analysis,according to an exemplary embodiment. In act 1310, log files are writtenby each thread in the system. In act 1320, a subset of the log files isparsed by the log parser. In an act 1330, the log parser writes thevalue of each field of interest in each log file entry into acorresponding field in a corresponding table in a database. In an act1340, the front end executes user-selected or user-generated databasequeries, and, in an act 1350, the user interface displays the results.Although the acts are described in a particular order in this example,the invention is not limited to acts occurring in this order, and someor all of the acts may take place in a different order, or in parallel.

V. Dial Plan for Outgoing Calls

On occasion a need may arise for an agent to make an outbound call froman agent device, e.g., to another agent in the contact center or to acustomer who has asked to be called back. In such a case a dial plan maybe provided by the feature server 425 (FIG. 4) to support the process ofconnecting the call. FIG. 14 shows a schematic diagram of an exemplarygeographically distributed contact center, which may include two datacenters 200, one in New York, and one in London, and it may include fiveagent sites 210, located in Daly City, Menlo Park, N.Y., London, andParis.

FIG. 15 illustrates calling profiles, categories, and patterns, whichmay be used to implement a dial plan in one exemplary embodiment. Anagent may dial a sequence of digits referred to as a dialed string, andthe feature server 425 may classify it according to a set of categories,each of which may contain one or more patterns. For example, a firstcategory 1505 may include internal numbers, e.g., numbers correspondingto endpoints within the contact center, which may be five-digitextension numbers represented in a symbolic pattern-matching notation as“XXXXX”, where the symbol “X” denotes a position in the dialed stringfor which any digit constitutes a match. A second category 1510 mayinclude emergency numbers, represented by the two patterns “9 911” and“911”. A third category 1515 may include local external numbers, afourth category 1520 may include external domestic numbers, a fifthcategory 1525 may include external international numbers, and a sixthcategory 1530 may include blocked numbers. Blocked numbers may include,for example, numbers with a “900” area code, for which additionalcharges may be levied on the calling party.

Each agent device from which outbound calls can be made may beconfigured with one or more calling profiles, each of which is a list ofavailable categories, e.g., categories available for matching. Eachcategory may contain a set of patterns. The calling profile may be usedto limit the ability of the agent device to place outgoing calls. When asequence of digits is dialed at an agent device, the sequence, e.g., thedialed string, may be tested against each pattern in each categoryincluded in the profile (e.g., each available category) to determinewhether the dialed string matches any pattern in the category. If thedialed string does not match any pattern in a category in the callingprofile, or if it matches any pattern in a blocked category, the callwill be denied, and the agent device may generate an error tone toindicate that the call has been denied.

For example, a first calling profile 1535, which may be referred to as alocal calling profile, may include the first category 1505, the secondcategory 1510, and the third category 1515. Any call attempted from anagent device configured with the first calling profile will be deniedunless the dialed string matches a pattern in the first category, thesecond category, or the third category, e.g., unless the call is aninternal call, a call to an emergency number, or a call to a localexternal number. In this case the inclusion or exclusion of the sixthcategory, containing a pattern for blocked “900” numbers, may have noeffect because a number beginning with “9-1-900” and followed by 7 otherdigits will in any event not match any of the patterns in the categoriesin the calling profile. A second calling profile 1540 may contain thefirst category 1505, the second category 1510, the third category 1515,the fourth category 1520, and the sixth category 1530, so that an agentdevice configured with the second calling profile 1540 may be able toinitiate calls to internal numbers, emergency numbers, local externalnumbers, and domestic external numbers. International calls may not bepossible because an attempt to dial an international number may resultin a dialed string not matching any pattern in a category associatedwith the calling profile, and an attempt to dial a “900” number may failas a result of it matching the blocked sixth category 1530. Callingprofile definitions may be different for different agent sites 210, sothat, for example, the definition of a local calling profile in a DalyCity agent site 210 may be different from the definition of a localcalling profile in a Menlo Park agent site 210. The definitions ofcategories may similarly be different for different agent sites 210.

If the dialed string matches more than one category, then a rank, whichmay be referred to as a weight, may be used to identify the category andpattern which is the best match for the dialed string. In one exemplaryembodiment the weight is calculated as follows. First, a maximum dialedstring length, which is at least the length of the longest anticipateddialed string, is selected. The weight is initially set to this maximumdialed string length multiplied by 10. Then, for each digit element in apattern, the weight is decreased by the number of digits, out of apossible 10 (ranging from “0” to “9”) that will match that digitelement. Here, a digit element is an element of a pattern correspondingto one digit of a dialed string; the element matches a range of possiblevalues for that digit. For example, in one notation the character “X”matches any digit, “Z” matches any digit except “0”, and a range may bespecified in brackets, so that “[2-9]” matches any digit between “2” and“9”. Using this algorithm and a maximum dialed string length of 100, apattern such as “9 [2-9]XX XXXX” has an initial weight of 1000 (e.g.,100×10), which is then decreased by 1 (for the initial “9” which matchesone digit), then by 8 (for the digit element “[2-9]” which matches eightpossible digits), and then by 60 (for the six “X” digit elements, eachof which matches ten possible digits), resulting in a weight of 931. Inone notation the character “*” may match any number of digits having anyvalue, so that for example “9*” matches any dialed string beginning withthe digit “9”. The weight of this pattern may be calculated assuming thedialed string has the maximum length, so that for a maximum dialedstring length of 100, the weight is 9. In this case the weight iscalculated from an initial weight of 1000 (e.g., 100×10), decreased by 1(for the initial character “9”) and decreased by 990 (for the remaining99 “*” characters, each of which matches 10 possible digits). Although aspecific example of an algorithm for calculating a weight for a patternis described here, the invention is not limited thereto, and otheralgorithms may be used to determine the weight of a pattern. In oneembodiment, the weight of a pattern may be determined using an algorithmwhich takes as input both the pattern and the dialed string.

Once the dialed string has been matched to one or more category and thebest match category has been identified, e.g., the category with thehighest weight, or any blocking category, the dialed string istranslated into a translated string, which may include both routinginformation and an endpoint identifier. For example if the dialed stringis a domestic external number, the call may be routed part way to itsdestination within an internet protocol (IP) network, through a gateway312 to the PSTN network, and from there to the destination number. ThePSTN carrier may charge for the use of the PSTN network, and the amountcharged, e.g., the cost to the contact center operator, may depend onmultiple factors, including the time of day, the day of the week, andthe location of the gateway and of the destination number. Differentgateways 312 may be serviced by different PSTN carriers, and severalPSTN carriers may be available at a gateway 312. The time of day, whichmay affect the cost of the call, may depend on the time zone in whichthe gateway is located.

In one exemplary embodiment, the feature server 425 (FIG. 4) maintainsstate information on a set of gateways 312, including, for example,whether the gateway 312 is operational and its reserve capacity. Whentranslating a dialed string with an endpoint external to the contactcenter, the feature server 425 first identifies available gateways 312,e.g., those that are operational and have the capacity to handle anadditional call, and it then calculates the estimated cost of using eachavailable gateway to route the call, taking into account the carriersavailable at the gateway, the time of day, the day of the week, the timezone in which the gateway 312 is, and any other factors, such as thedistance from the gateway 312 to the location of the destination number.The feature server 425 then selects the lowest-cost option, andtranslates the number accordingly.

The output of the translation process may be a string referred to as atranslated number which may include an identifier for the destinationnumber, e.g., an E.164 number, and other characters identifying therouting to the PSTN. For example, if the feature server 425 determinesthat the call is best routed through a New York gateway identified bythe string “NY1” it may form, from a dialed string such as “212 5551234”, the translated number “NY1 212 555 1234”.

Although exemplary embodiments of a SIP cluster have been specificallydescribed and illustrated herein, many modifications and variations willbe apparent to those skilled in the art. Accordingly, it is to beunderstood that SIP cluster constructed according to principles of thisinvention may be embodied other than as specifically described herein.For example, the present invention need not be limited to use in acontact center; it may provide benefits in other applications such asenterprise communications systems used for other purposes. The inventionis also defined in the following claims, and equivalents thereof.

What is claimed is:
 1. A method for adding a first server to a group ofexisting second servers associated with a contact center, the methodcomprising: sending by the first server a request for initiatingaddition of the first server to the group of existing second servers;sending, by each of the plurality of existing second servers, inresponse to the request, state information for a resource mapped to theexisting second server, the state information being transmitted to thefirst server without sending the state information to one of theexisting second servers; and sending, by the first server, a commitmessage to each of the existing servers, in response to receiving thestate information from each of the plurality of existing second servers;and changing the mapping of one of the resources from one of theexisting second servers to the first server in response to the commitmessage.
 2. The method of claim 1, comprising: sending, by the firstserver, to each of the plurality of existing second servers, an initiatemessage; sending, by each of the plurality of existing second servers,to the first server, an initiation acknowledge message; and sending, bythe first server, to each of the plurality of existing second servers, astate transfer request.
 3. The method of claim 1, comprising: notifyinga configuration server, responsible for maintaining a list of servers,of the addition of the first server; updating, by the configurationserver, the list of servers; and notifying, by the configuration server,a set of subscribers of the update to the list of servers.
 4. The methodof claim 1 further comprising: receiving a request associated with aresource mapped to the first server from the existing second servers;identifying the first server as responsible for the resource; androuting the request to the first server in response to the identifying.5. The method of claim 4, wherein the resource is a directory number(DN).
 6. The method of claim 4, wherein the identifying of the firstserver as responsible for the resource comprises: providing, to afunction, a resource identifier (ID) identifying the resource; andreceiving as an output from the function a module identifier (ID) forthe first server.
 7. The method of claim 6, wherein the function is ahash function.
 8. The method of claim 7, wherein the hash function is aconsistent hash function.
 9. The method of claim 8, wherein the hashfunction comprises: a first basic hash function configured to mapresource identifiers into a range; and a second basic hash functionconfigured to map module identifiers into the range.
 10. The method ofclaim 9, wherein the second basic hash function is further configured tomap a replica of each module identifier into the range.
 11. The methodof claim 7, wherein the hash function is configured to map resourceidentifiers corresponding to resources in a geographic region intomodule identifiers corresponding to servers executing on computingdevices in the geographic region.
 12. A method for removing a firstserver from a group of servers associated with a contact center, thegroup of servers including the first server and a plurality of othersecond servers, the method comprising: sending by the first server arequest for initiating removal of the first server from the group ofservers; sending, by the first server, state information for a resourcemapped to the first server, the state information being transmitted bythe first server without state information being transmitted by one ofthe other second servers; and sending, by the first server, a commitmessage to each of the other second servers; and changing the mapping ofone of the resource from the first server to one of the other secondservers to the first server in response to the commit message.
 13. Themethod of claim 12, comprising: sending, by each of the plurality ofother second servers, to the first server, an initiation acknowledgemessage.
 14. The method of claim 12, comprising: notifying aconfiguration server, responsible for maintaining a list of servers, ofthe removal of the first server; updating, by the configuration server,the list of servers; and notifying, by the configuration server, a setof subscribers of the update to the list of servers.
 15. The method ofclaim 12, further comprising: receiving a request associated with aresource mapped to a remaining server of the plurality of other secondservers from the first server; identifying the remaining server asresponsible for the resource; and routing the request to the remainingserver in response to the identifying.
 16. The method of claim 15,wherein the identifying of the remaining server as responsible for theresource comprises: providing, to a function, a resource identifier (ID)identifying the resource; and receiving as an output from the function amodule identifier (ID) for the remaining server.
 17. The method of claim16, wherein the function is a hash function.
 18. The method of claim 17,wherein the hash function is a consistent hash function.
 19. The methodof claim 18, wherein the hash function comprises: a first basic hashfunction configured to map resource identifiers into a range; and asecond basic hash function configured to map module identifiers into therange.
 20. The method of claim 19, wherein the second basic hashfunction is further configured to map a replica of each moduleidentifier into the range.
 21. The method of claim 17, wherein the hashfunction is configured to map resource identifiers corresponding toresources in a geographic region into module identifiers correspondingto servers executing on computing devices in the geographic region.